NEW ORLEANS - (AP) — A fire raging in a coastal Louisiana bayou where a tugboat struck a gas pipeline appeared to have diminished Wednesday night, but is far from extinguished, the Coast Guard said.

Smoke was still visible in New Orleans, 30 miles to the north, and officials say they don't expect the fire sparked by Tuesday night's crash to be out until Thursday or later.

It started when a tug pushing an oil barge struck a liquefied natural gas pipeline in shallow Bayou Perot, where Lafourche and Jefferson parishes meet. Four people were injured, one critically.

No oil had spilled as of Wednesday evening and what appeared to be pockets of oil on the water turned out to be ash from the burned gas, the Coast Guard said.

At a news conference, Capt. Jonathan Burton stressed that the barge remained intact and none of the oil appeared to be leaking. However, as a precaution, protective boom was deployed in the area around the site and in nearby environmentally sensitive areas. Oil skimmers were also dispatched.

"We're not waiting for something to happen," Burton told reporters. Preparations included consulting with the National Oceanic and Atmospheric Administration on where currents might take the oil if it were released.

Pipeline owner Chevron cut off the flow of gas to the pipeline. But the affected section was 19 miles long and was expected to burn for some time. Coast Guard Petty Officer William Colclaugh said Chevron had begun an operation to inject nitrogen gas into the line to help extinguish the blaze, but it was unclear when and how that would affect the fire. In the meantime, Colclaugh said, efforts were concentrated on keeping the oil-laden barge cool, to avoid a worse fire and the release of any oil.

Three of those injured had been hospitalized, treated and released but one was taken to a Baton Rouge burn unit and was in critical condition, the Coast Guard said. Their identities were not released.

The area where the crash happened is thinly populated and no evacuations were ordered.

Burton said investigators hadn't determined why the tug, owned by Settoon Towing, hit the pipeline. The Coast Guard estimated water at the site to be 2 or 3 feet deep.

Asked specifically if the tug, the Shanon E. Settoon, was outside navigation channels, Burton would only say the accident was under investigation.

Environmental company ES&H of Houma was hired by Settoon Towing for cleanup. "The barge appears to be intact and the integrity is OK," Patrick Bergeron of ES&H said at a news conference. The boom was a precaution, he said.

The area is along the northern reaches of Barataria Bay, which was heavily affected by oil from the BP spill in 2010. It is mostly small communities where people often make their living from the sea, either working in the oil and gas industry or as fishermen.

The 92,000 gallons the Coast Guard says was being carried by the barge is a fraction of the millions of gallons that spewed into the Gulf of Mexico during the 2010 spill.

The region where the fire was burning is crisscrossed by pipelines. Wellheads are a common sight in the shallow waters of the bayou and bay shoreline.

Bayou Perot was the scene of an explosion and fire on a specialized oil rig in December 2010 in which three men were injured. The explosion happened while the men were welding and there was no pollution, the Coast Guard reported.

Another Settoon tug was involved in a February 2012 collision on the Mississippi River that resulted in less than 10,000 gallons of oil spilling into the river. The Coast Guard said the spill resulted from a collision between a barge pushed by the Clarence W. Settoon and a construction barge pushed by another tug about 50 miles upriver from New Orleans.